GLOBAL NAVIGATION SATELLITE SYSTEM (GNSS).

Performed by: Zhakypbek D

GlobalNavigationSatelliteSystem
(GNSS)referscollectivelytothe
worldwidepositioning,navigationand
timing(PNT)determination
capabilitiesavailablefromoneormore
satelliteconstellations.Currentlythe
UnitedStatesGPSandtheRussian
FederationsGlobalnaya
NavigatsionnaySputnikovayaSistema
(GLONASS)canbedescribedas
GNSS.Inthefuture,European
UnionsGalileo,ChinasCOMPASS
(BeiDou)andothersystemscapableof
beingusedtoprovidePNTservices
globallymaybeconsideredasGNSS.
 GNSS ELEMENTS
1.2.2Thesatellitesinthecoresatelliteconstellationsbroadcastatimingsignal
andadatamessage
thatincludestheirorbitalparameters(ephemerisdata).AircraftGNSS
receiversusethesesignalstocalculate
theirrangefromeachsatelliteinview,andthentocalculatethree-dimensional
positionandtime.
1.2.3TheGNSSreceiverconsistsofanantennaandaprocessorwhich
computesposition,timeand,
possibly,otherinformationdependingontheapplication.Measurementsfrom
aminimumoffoursatellitesare
requiredtoestablishthree-dimensionalpositionandtime.Accuracyis
dependentontheprecisionofthe
measurementsfromthesatellitesandtherelativepositions(geometry)ofthe
satellitesused
Theexistingcoresatelliteconstellationsalonehoweverdonotmeetstrictaviationrequirements.
Tomeettheoperationalrequirementsforvariousphasesofflight,thecoresatelliteconstellations
require
augmentationintheformofaircraft-basedaugmentationsystem(ABAS),satellite-based
augmentation
system(SBAS)and/orground-basedaugmentationsystem(GBAS).ABASreliesonavionics
processing
techniquesoravionicsintegrationtomeetaviationrequirements.Theothertwoaugmentations
useground
monitoringstationstoverifythevalidityofsatellitesignalsandcalculatecorrectionstoenhance
accuracy.
SBASdeliversthisinformationviaageostationaryearthorbit(GEO)satellite,whileGBASuses
aVHFdata
broadcast(VDB)fromagroundstatio
3.2.1 Global Positioning
System (GPS) 3.2.1.1 GPS is
a satellite-based radio
navigation system which
utilizes precise range
measurements from GPS
satellites to determine
position and time anywhere
in the world. The system is
operated for the
government of the United
States by the United States
Air Force. In 1994, the
United States offered the
GPS standard positioning
service (SPS) to support the
needs of international civil
aviation and the ICAO
Council accepted the offer.
comprised of 24 satellites in six
orbital planes. The satellites operate
in near-circular 20 200 km (10 900
NM) orbits at an inclination angle of
55 degrees to the equator; each
satellite completes an orbit in
approximately 12 hours. The GPS
control segment has five monitor
stations and four ground antennas
with uplink capabilities. The monitor
stations use a GPS receiver to
passively track all satellites in view
and accumulate ranging data. The
master control station processes this
-2 Global Navigation Satellite System
(GNSS) Manual information to
determine satellite clock and orbit
states and to update the navigation
message of each satellite. This
updated information is transmitted to
the satellites via the ground antennas,
which are also used for transmitting
The GPS SPS performance standard
defines the level of performance that
the United States Government
commits to provide to all civilian
users. The Interface Control
Document (ICD) GPS 200C details the
technical characteristics of the SPS L-
band carrier and the C/A code as well
as the technical definition of
requirements between the GPS
constellation and SPS receivers.
Additional information concerning
GPS can be found on the United
States Coast Guards Navigation
Center (NAVCEN) website
(www.navcen.uscg.gov).
GLONASS provides three-dimensional position and velocity
determinations based upon the measurement of transit time and
Doppler shift of radio frequency (RF) signals transmitted by
GLONASS satellites. The system is operated by the Ministry of
Defence of the Russian Federation. In 1996, the Russian
Federation offered the GLONASS channel of standard accuracy
(CSA) to support the needs of international civil aviation and the
ICAO Council accepted the offer. 3.2.2.2 The nominal GLONASS
space segment consists of 24 operational satellites and several
spares. GLONASS satellites orbit at an altitude of 19 100 km (10
310 NM) with an orbital period of 11 hours and 15 minutes. Eight
evenly spaced satellites are to be arranged in each of the three
orbital planes, inclined 64.8 degrees and spaced 120 degrees
apart
A navigation message transmitted from each satellite
consists of satellite coordinates, velocity vector
components, corrections to GLONASS system time, and
satellite health information. Measurements from a
minimum of four satellites are required to establish three-
dimensional position and time. A minimum of three
satellite measurements is required to determine a two-
dimensional position and time, if altitude is known. The
users receiver may track these satellites either
simultaneously or sequentially. GLONASS satellites
broadcast in two L-band portions of the RF spectrum and
have two binary codes, namely, the C/A code and the P-
code, and the data message. GLONASS is based upon a
frequency division multiple access (FDMA) concept.
GLONASS satellites transmit carrier signals at different
frequencies. A GLONASS receiver separates the total
incoming signal from all visible satellites by assigning
different frequencies to its tracking channels. The use of
The navigation data message
provides information regarding
the status of the individual
transmitting satellite along with
information on the remainder of
the satellite constellation. From a
users perspective, the primary
elements of information in a
GLONASS satellite transmission
are the clock correction
parameters and the satellite
position (ephemeris). GLONASS
clock corrections provide data
detailing the difference between
the individual satellites time and
GLONASS system time, which is
referenced to Coordinated
Universal Time (UTC).
The GLONASS control segment performs satellite monitoring and control
functions, and determines the navigation data to be modulated on the coded
satellite navigation signals. The control segment includes a master control
station and monitoring and upload stations. Measurement data from each
monitoring station is processed at the master control station and used to
compute the navigation data that is uploaded to the satellites via the upload
station. Operation of the system requires precise synchronization of satellite
clocks with GLONASS system time. To accomplish the necessary
synchronization, the master control station provides the clock correction
parameters.
Three augmentation systems, namely aircraft-based augmentation
system (ABAS), satellite-based augmentation system (SBAS) and
ground-based augmentation system (GBAS), have been designed and
standardized to overcome inherent limitations in GPS and GLONASS.
RAIM algorithms require a minimum of five visible satellites in order to
perform fault detection and detect the presence of an unacceptably large
position error for a given mode of flight. FDE uses a minimum of six satellites
not only to detect a faulty satellite but also to exclude it from the navigation
solution so that the navigation function can continue without interruption.
3.3.2.3 A barometric altimeter may be used as an additional measurement so
that the number of ranging sources required for RAIM and FDE can be
reduced by one. Baro aiding can also help to increase availability when there
are enough visible satellites, but their geometry is not adequate to perform
integrity function. Basic GNSS receivers require the use of baro aiding for
non-precision approach operations.
The inputs to the RAIM and FDE algorithms are the standard
deviation of the measurement noise, the measurement geometry, as
well as the maximum allowable probabilities for a false alert and a
missed detection. The output from the algorithm is the horizontal
protection level (HPL), which is the radius of a circle centred at the
true aircraft position that is guaranteed to contain the indicated
horizontal position within the specified integrity requirement.
 The availability of RAIM and FDE will be
slightly lower for mid-latitude operations
and slightly higher for equatorial and
high latitude regions due to the nature of
the orbits. The use of satellites from
multiple GNSS elements (e.g. GPS +
GLONASS) or the use of SBAS satellites
as additional ranging sources can
improve the availability of RAIM and FDE.
 As defined in the SARPs, SBAS has the potential to
support en-route through Category I precision approach
operations. Initial SBAS architectures will typically
support operations down to approach procedures with
vertical guidance (APV). 3.3.3.2 SBAS monitors GPS
and/or GLONASS signals using a network of reference
stations distributed over a large geographic area. These
stations relay data to a central processing facility, which
assesses signal validity and computes corrections to the
broadcast ephemeris and clock of each satellite. For each
monitored GPS or GLONASS satellite, SBAS estimates the
errors in the broadcast ephemeris parameters and
satellite clock, and then broadcasts the corrections
SBAS uses two-frequency range
measurements to estimate the ranging
delay introduced by the Earths
ionosphere, and broadcasts the
corrections applicable at predetermined
ionospheric grid points. The SBAS
receiver interpolates between grid
points to calculate the ionospheric
correction along its line-of-sight to each
satellite.
3.3.4 Ground-based Augmentation
System (GBAS) 3.3.4.1 As defined in
the SARPs, GBAS will support
Category I operations and the
provision of GBAS positioning service
in the terminal area. It has the
potential to support precision
approach operations down to
Categories II and III and some surface
movement operations. 3.3.4.2 The
GBAS ground facility monitors GPS
and/or GLONASS signals at an
aerodrome and broadcasts locally
relevant integrity messages,
pseudorange corrections and
approach data via a VHF data
broadcast (VDB) to aircraft within the
nominal range of 37 km (20 NM) in
the approach area (when supporting
Category I operations) and within the
range depending upon intended
operations (when providing
positioning service). When an SBAS
 GNSS IMPLEMENTATION 5.1 GENERAL The
implementation of GNSS operations requires that
States consider a number of elements. This
chapter describes the following elements: a)
planning and organization; b) procedure
development; c) air traffic management (airspace
and air traffic control (ATC) considerations); d)
aeronautical information services; e) system
safety analysis; f) certification and operational
approvals; g) anomaly/interference reporting;
and h) transition planning